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Frosts and Freezes not over, oh my!

Posted: March 27, 2014 4:58 p.m.
Updated: March 28, 2014 5:00 a.m.

To say these past few months have been cold is an understatement and while my northern roots have relished getting my wool sweaters out of the cedar chest, our trees and other plants have not had the ability to bundle up for warmth. No matter how you slice it, our woody friends have been exposed to dramatically cold temperatures this winter and even though spring is officially here, we have yet to see how Mother Nature’s wintery touch has affected (or may still affect) all things green.

Before exploring the possible damage to plants and trees, let’s revisit (in writing only) just how cold it was. According to the National Weather Service Forecast Office in Columbia, our first predicted frost date was October 1, 2013. A frost is likely to occur when the predicted temperature is expected to fall to 36 degrees or lower within a three to 30 hour time frame. In actuality, the Columbia Metro Airport (where weather data is officially recorded for the Midlands) recorded a low of 30 degrees on October 26, 2013. This went beyond a frost to a freeze and was our first glimpse that Old Man Winter was on his way.

A freeze, according to the Farmer’s Almanac, is likely to occur when the temperature is expected to fall to 32 degrees or lower in a three to 30 hour time-frame. Freezes can be further defined as light, moderate and severe. The importance of these temperature classifications is to predict the effects of the cold to plants. As such, a light freeze is temperatures ranging from 29 degrees to 32 degrees, in which tender plants are killed but with little destructive effect on other vegetation. A moderate freeze is temperatures ranging from 25 degrees to 28 degrees in which destruction occurs to most vegetation, with especially heavy damage to fruit blossoms and tender and semi-hardy plants. A severe freeze is temperatures 24 degrees and colder in which heavy damage occurs to most plants.

This past November, the Columbia Metro Airport recorded 4 days when the morning lows were at or below 32 degrees. The coldest morning being 22 degrees, the first of the severe freezes. December brought us seven days at or just below 32 degrees. The coldest morning being 25 degrees, the first moderate freeze. In January, the New Year plunged us into artic-like weather with half the month measuring at or below 32 degrees for the overnight temperature. Nine out of those 15 days were below 23 degrees, exposing plants to more severe freezing! The lowest temperature for the month was 11 degrees; now that’s beyond cold! February was much milder (comparatively) with only five days at or below 32 degrees, but still had one frigid morning of 26 degrees (a moderate freeze). March has been predictably unpredictable and so far has brought us approximately seven days at or just below 32 degrees (light freezes). Will it ever end?

So, just how much damage was there to freeze-affected shrubs and trees? The answer is, “It depends.” The degree of damage to plant twigs, buds or roots depends on plant age, health prior to the freeze, cold tolerance of the plant and its location in the landscape. A very young or over-mature plant may be more susceptible to cold damage compared to one in its prime. If a tree or plant was vigorous and healthy last year, it will hopefully put out a full set of leaves this year. If a particular tree or plant was stressed, in declining health or perhaps newly transplanted prior to the deep freeze, you may see further stress or decline. Plants in this situation have less stored energy reserves and may not recuperate as well as their counterparts. In addition, some plants and trees are just more cold hardy than others. For example, when we take traditional coastal species such as live oaks, palms and oleander and plant them inland, they will eventually be exposed to extreme temperatures that their genetics are not engineered to withstand.

As we move forward into spring we can begin to assess any damage to our plants and trees. It’s as simple as looking around. As the ever-so-brief bursts of warm and wet weather wakes dormant flower and leaf buds, look for signs of life. Another way to determine if a plant is still alive is to gently scratch with your fingernail a small area of the bark on a twig or stem. If there’s green around the edges of the exposed wood, that part is still alive. If it’s brown and brittle, then it’s dead. From what I’ve seen so far, the sub-freezing temperatures have affected various plants and shrubs but ultimately only time will tell the degree of frost-bite damage.

What should you do if you have a shrub or tree with winter dieback? If the damage is obvious (no flowering or flushing out of leaves) then it’s ok to prune the deadwood. Be careful not to cut any more than necessary as removing any live tissue may further stress the plant. Many times though, it’s best to wait and see how much of the plant or tree flushes out new growth. In general, this process is complete by late May; at which time, you’ll be able to see either how much to prune or if the plant in question needs to be removed.

For those anxious to get outside and start planting or if you’ve already gotten your hands in the dirt and planted new flowers, trees or vegetables be mindful of spring frosts and freezes. Succulent, new growth or delicate flowers can be burned and killed as a result. Here are a few tips to protect your already established or new additions to your landscape:

First, watch the calendar and the forecast -- As mentioned, spring frosts are likely to occur before it’s all said and done. April 19th is our last official frost/freeze date, so there may be more frigid nights ahead. Cool, clear nights with low humidity, often following a cold front, are signs of an impending frost so keep tuned into the weather forecast.

Second, irrigate before the frost -- Studies indicate that a moist soil can hold four times more heat than a dry soil. It will also conduct heat to the soil surface faster than a dry soil, aiding in frost prevention. Thus, plants should be well watered, but not saturated, the day before a frost/freeze.

Third, mulch, mulch, mulch -- If you are inclined to rake away leaves or old pine straw from landscape beds or individual trees, wait! Mulch such as pine straw, shredded hardwood or leaves, helps insulate fibrous roots, the ones responsible for absorbing essential water and nutrients. These roots grow within the upper 4 inches of soil and are vulnerable to cold damage. A good 3- to 4-inch layer should be spread under the canopy of trees and shrubs. Be careful not to pile it against the stem or trunk as this may encourage disease or insect pest occurrence. Overall, mulch will help prevent soil temperatures from staying below freezing for long periods. Plants whose roots have frozen over the winter, may flush out this spring but then suddenly wilt and decline.

Fourth, don’t fertilize -- Fertilizing too early in the spring may encourage pre-mature plant growth, making your plants and trees more susceptible to cold damage. Instead, wait until after the last frost date (April 19) and get a soil sample analysis (available via Clemson Ext. Service) to determine if fertilization is even necessary.

Fifth, cover your plants and small trees (if possible) -- Covering plants can give you 2 to 5 degrees protection. Covers can be laid over the plant or can be supported on stakes. The difference being that protection is less wherever the cover physically touches the plant. Any material can be used to cover plants; however woven fabrics such as old towels, sheets and blankets are better insulators than plastics, paper or cardboard. If that’s all you have available though, better to use that than nothing. The best time to apply cover is in the late afternoon and should be removed the next morning once the sun comes up. Note that the point of covering plants is to trap the earth’s heat, not the plant’s heat so it is best not to cinch up the bottom of the covering as it will deter the heating affect.

Lastly, if you have a valuable, rare or specialty plant or small tree, the use of a 60 watt light bulb placed under a covering may be considered. This will provide addition warmth and protection but be careful that the light bulb does not touch the plant.

Unfortunately, we can’t undo Mother Nature’s blow from winter or stop any spring freezes.

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